In large distribution applications, sortation conveying systems are typically used to fulfill orders of intermingled articles such as assortments of books, video cassette containers, packaged software, compact disc containers, etc. Workers load items into the system and the articles are conveyed in single file within individual pockets on a core conveyor belt. As the assorted articles begin to move through the system on the core conveyor belt, the system reads preprinted bar code information and automatically sorts the articles into various outgoing orders. The downstream end of the sortation conveyance system normally includes a system of computer controlled diverting gates that divert articles into appropriate stacking stations for outgoing orders. Outgoing orders typically contain 100 or more articles. If an article is loaded onto the core conveyor, and it is not needed for any of the outgoing orders, it is discharged into a left over bin and returned to stock.
The assignee of the present application has developed an improved stacking station in which articles for a particular order are stacked onto an elongated and substantially horizontal accumulation tray. The articles are stacked sequentially onto the tray such that the articles are standing upright on edge, and in series side-by-side. This system is disclosed in detail in copending patent application Ser. No. 09/439,862 entitled "Discharge Stacking Station for Sortation Conveying System" by David A. Remsing, Jason M. Knas and Todd R. Eggebrecht filed on Nov. 12, 1999 incorporated herein by reference.
The disclosed discharge stacking station includes an accumulation tray that has substantial length in order to accommodate large orders of articles (e.g. preferably about 4-12 feet). The accumulation tray extends from the loading mechanism for the stacking station perpendicularly outward, and workers unload the articles for a particular order from the opposite end of the accumulation tray. Preferably, the tray has a bottom wall and a backstop wall which extends perpendicularly upward from a rear edge of the bottom wall. The bottom wall of the accumulation tray is preferably tilted downward towards the rear edge so that the force of gravity assists the alignment of articles in the accumulation tray (e.g., alignment along the bottom wall and the back wall).
As disclosed in the above referenced copending application, the stacking station preferably includes a dead plate on the accumulation tray which acts much like a bookend to stabilize the series of articles being stacked onto the accumulation tray. The dead plate is connected to a pneumatic cylinder that moves the dead plate linearly along the horizontal length of the accumulation tray. Before the first article is stacked onto the accumulation tray, the dead plate is positioned near the loading end of the accumulation tray. Then, the pneumatic cylinder is deactivated (i.e. the dead plate is connected to a dead cylinder). When the articles are being stacked onto the accumulation tray, the dead plate abuts the first stacked article to prevent tipping of the article in the accumulation tray. As additional articles are stacked onto the accumulation tray, the dead plate attached to the dead cylinder moves incrementally along the accumulation tray. It has been found that use of a dead cylinder provides the dead plate with sufficient resistance to prevent tipping of the articles in the accumulation tray during the stacking procedure, yet does not interfere with the loading of articles onto the accumulation tray. When the order is complete, the attending worker unloads the articles from the accumulation tray. After the articles have been unstacked, the dead plate is returned to the home position ready to accept the next order being stacked onto the accumulation tray. Although the system as disclosed in the above copending patent application is effective, it has been found that it would be desirable to further improve the efficiency of workers unloading articles from the accumulation tray.